In some telecommunication protocols, objects of a multimedia data stream (i.e. a set of sequences of bits that must all be communicated in the same period of time so as to jointly convey information, for example an audio clip object synchronized with a video clip object) are subjected to an overall size constraint, i.e. the total number of bits in the multimedia data stream is not permitted to exceed some number of bits. Such a constraint may be due to the protocol itself, or due to other factors such as limitations of the device sending or receiving the multimedia data stream (e.g. the size of memory included in either of the devices). An additional or alternative constraint may exist if one or more communication channels used in communicating the message are subject to a maximum rate limitation. Corresponding to the maximum allowed data rate and/or size are maximum allowed sizes of the different objects making up the multimedia data stream. Thus, in a telecommunication system providing a channel or set of channels (each possibly subject to an individual or collective rate limitation) for communication of a multimedia data stream, there is a data size budget that must be adhered to, or a corresponding data rate allowance that must not be exceeded. In other words, in a multimedia data stream conveying N objects, the rates/sizes Ri of the different individual objects i making up the multimedia data stream must be such that,             ∑              i        =        1            N        ⁢                   ⁢          R      i        ≤      R    M  where RM is a maximum allowed total data rate/size.
In view of such a limitation, given a set of different types of objects to be communicated over a telecommunication system, the problem arises as to how best to encode the different objects so as to have a total data rate/size less than or equal to the maximum allowed total data rate/size, and yet have a high overall quality according to some measure of quality. Although quality is generally understood to be subjective, it is reasonable to suppose that the overall quality of a multimedia data stream is higher if the different types of objects making up the multimedia data stream are all communicated so as to have roughly the same quality, as opposed to a data stream in which say one object (e.g. a video clip) is communicated so as to have a high quality, and another object, of more or less equal importance (e.g. a corresponding audio clip), is communicated so as to have a poor quality.
Thus, what is needed is a solution to the problem of how to encode the different objects of a multimedia data stream so as to provide a high overall quality, at least according to some reasonable measure of overall quality, and yet to make possible communicating the multimedia data stream by ensuring that its total rate/size is sufficiently low.